Multi-Leg
General
A Multi-Leg trade is one that consists of two or more legs. A multi-leg trade can consist of options trades as well as stock.
Buying a call would be a single leg trade. Opening a call debit spread (buy one call, sell one call of a higher strike) would be a multi-leg options trade with two legs.
Another example of a 2-legged options trade would be a straddle, which involves both a call and put option.
An example of a 3-legged options trade would be a long call butterfly, which involves 3 call options of varying strike prices.
An example of a 4-legged options trade would be a short iron condor, which involves 2 call options of varying strike prices as well as 2 put options of varying strike prices.
By definition a Roll is also a multi-leg options trade.
A multi-leg stock trade is a trade that consists of one option leg and one stock leg. An example of this would be a call-write (buy 100 shares, write 1 call).
Multi-Leg Trades and Unusual Whales
Check out this Youtube video: Spotting and Understanding Multileg Options Trades on Unusual Whales!
When a multi-leg trade is executed that trade is given a specific ‘Trade Code’ which identifies as being a multi-leg trade (usually prefix ML). These codes also differentiate between multi-leg options and multi-leg stock trades.
Single Leg trades will be identified by SL in the feed. Multi-leg options trades will be labeled ML-O. Multi-leg stock trades will be labeled ML-S.
Nothing explicitly states that a trade is connected to another. However, the Unusual Whales flow feed attempts to group linked trades. You can also often figure out which trades are linked based on the trade execution time as well as the sizing of the trades.
You can view other trades that may be multi-legged with the one in your feed by clicking ML-O or ML-S, or the respective icon in the flow feed.
For ML-S trades the stock leg will only be shown if it has taken place on a NASDAQ exchange.
The % of a contract's volume that was from multi-leg trades is a data point available in the contract historical volume/OI data.
You can learn more about spotting multi-leg trades in the Flow Feed by watching the YouTube video on shortcut links.